1. Field of the Invention
The present invention relates to a surveying instrument having an optical distance meter.
2. Description of the Related Art
A conventional surveying instrument such as a total station has a function to measure the distance between two points and also horizontal and vertical angles. Such a conventional surveying instrument generally measures the distance between two points with a distance meter, usually an electronic distance meter (EDM) incorporated in or attached to the surveying instrument.
The electronic distance meter incorporates an optical distance meter which calculates the distance from the phase-difference or the time difference between a measuring light (externally-projecting light), which is projected toward a target, and an internal reference light. The optical distance meter includes a light-transmitting optical system for transmitting a measuring light to the target via the objective lens of a sighting telescope provided as a component of the electronic distance meter, and a light-receiving optical system for receiving light reflected by the target. The light-receiving optical system includes a wavelength selection filter for reflecting the measuring light which is reflected by the target to be passed through the objective lens of the sighting telescope, toward a light receiving element. The measuring light and the internal reference light are alternately incident on the light receiving element during operation of the optical distance meter.
To improve the precision of the optical distance meter by increasing the signal-to-noise ratio (S/N) of a signal of a received light, the light receiving element preferably receives only the measuring light and the internal reference light. However, in conventional surveying instruments which incorporates an electronic distance meter, it is sometimes the case that ambient light enters into the sighting telescope via the eyepiece thereof. This is a leading cause of deteriorating the precision of the optical distance meter.
The present invention has been devised in view of the problem noted above, and accordingly, an object of the present invention is to provide a surveying instrument having an optical distance meter, wherein ambient light which enters into the sighting telescope via the eyepiece thereof has no adverse effect on the precision of the optical distance meter.
To achieve the objects mentioned above, according to an aspect of the present invention, a surveying instrument is provided, including a sighting telescope for sighting an object; an optical distance meter which includes a light-transmitting optical system for transmitting a measuring light toward the object via the sighting telescope, a light-receiving optical system for receiving light reflected by the object, and a light-receiving element which receives the measuring light reflected by the object and received by the light-receiving optical system; and a light shield mask positioned on an optical axis between the eyepiece and the light-receiving element to cut off incoming rays from the eyepiece.
Preferably, the light-transmitting optical system includes a wavelength selection filter which reflects the measuring light reflected by the object and passed through an objective lens of the sighting telescope, in a forward direction along an optical path of the sighting telescope; and a mirror which reflects the measuring light reflected by the wavelength selection filter outside the optical path of the sighting telescope.
The light shield mask can be fixed to the wavelength selection filter. Alternatively, the light shield mask can be fixed to the mirror.
In an embodiment, the surveying instrument further includes a focus detecting device for detecting a focus state of the sighting telescope; and a controller for controlling the sighting telescope to automatically focus on the object in accordance with the focus state detected by the focus detecting device.
Preferably, the focus detecting device is a phase-difference detection focus detecting device which detects an in-focus state from a correlation between a pair of images respectively formed by two light bundles which are respectively passed through two different pupil areas of the phase-difference detection focus detecting device and passed through different portions of an objective lens of the sighting telescope. The light shield mask is positioned so as not to interfere with the two different pupil areas.
In an embodiment, the sighting telescope includes a focus adjustment lens having a negative power, which is moved in accordance with the focus state detected by the focus detecting device.
In an embodiment, the light shield mask is fixed to the focus adjustment lens.
In an embodiment, the wavelength selection filter reflects only a portion of light having specific wavelengths which is reflected by the object and passed through the objective lens.
Preferably, the mirror is made of a parallel-plate mirror having front and rear surfaces parallel to each other. The rear surface which faces the wavelength selection filter reflects the measuring light reflected by the wavelength selection filter toward the outside of the optical path of the sighting telescope.
In an embodiment, the objective lens of the sighting telescope is moved to bring the object in focus in accordance with the focus state detected by the focus detecting device.
According to another aspect of the present invention, a surveying instrument is provided, including a sighting telescope for sighting an object; a light emitting element which emits a measuring light toward the object via the sighting telescope; an optical distance meter having a light-receiving element which receives the measuring light reflected by the object and passed through an objective lens of the sighting telescope; and a light shield mask positioned on an optical axis between the eyepiece and the light-receiving element to cut off incoming rays from the eyepiece.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2000-138312 (filed on May 11, 2000) which is expressly incorporated herein by reference in its entirety.